For germinating seeds of the Sophora japonica (Japanese Pagoda Tree) bonsai, it is essential to maintain an appropriate soil temperature. According to various sources, the ideal temperature range for germination is between 60°F to 75°F (15°C to 24°C).

The care guide from Bonsai Empire emphasizes the importance of avoiding sudden temperature fluctuations and drafts, which can adversely affect the growth of the bonsai. Proper watering practices should also be maintained, particularly when the surface of the soil is dry. More on their recommendations can be found here.

For those looking to germinate Sophora japonica seeds, it is advised to sow the seeds about 1/4 inch deep and keep the soil consistently moist. It is also beneficial to mulch the seed bed and cover it with some shade to protect the growing seeds. Further details on the seed germination process can be explored in the guide provided by TreeHelp here.

In summary, ensuring a stable soil temperature within the recommended range, alongside proper watering and protection from excessive sunlight, will promote successful germination and growth of Sophora japonica seeds.

Sources

Care guide for the Sophora Bonsai tree (Japanese Pagoda Tree)What I should do for the Soil temperature when germinating cherry ...Sophora japonica | Indoor bonsai data sheetGrow trees from seed as Bonsai cultivation techniqueSophora japonica: Japanese Pagoda Tree Seeds - TreeHelpBonsai Beginner's weekly thread –2024 week 21 - RedditBonsai - Sephora Japonica | A plant by @GreenGeek on Greg

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